Disc brake for a commercial vehicle

ABSTRACT

A disc brake for a commercial vehicle includes a brake caliper which extends over a brake disc, a brake application device which is arranged in the brake caliper for pressing brake pads against the brake disc, and at least one adjustment spindle which is rotatably mounted in a bridge via a threaded coupling. A wear adjusting device is positioned in the brake caliper by which a wear-induced change of the clearance between the brake pad and the brake disc can be substantially compensated for via an axial movement of the adjusting spindle. The disc brake is designed such that the adjusting spindle has at least one axial groove on an outer side, the length of the groove being limited in the direction of the brake application device. A stop, which is axially fixed relative to the bridge, engages into the axial groove in a relatively displaceable manner.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT International Application No.PCT/EP2012/065853, filed Aug. 14, 2012, which claims priority under 35U.S.C. §119 from German Patent Application No. 10 2011 112 360.5, filedSep. 2, 2011, the entire disclosures of which are herein expresslyincorporated by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a disc brake for a commercial vehicle having abrake caliper which engages over a brake disc, a brake-applicationdevice which is arranged in the brake caliper and which serves forpressing brake pads against the brake disc, and at least one adjustmentspindle which is rotatably mounted, by way of a corresponding thread, ina bridge of the brake-application device.

In the case of a generic disc brake such as is known, for example, fromDE 94 22 342 U1, a brake lever acts on a bridge which is positioned in abrake caliper and in which there are mounted two adjustment spindles,which have in each case one thrust piece for the mounting of a brake padcomposed of a lining carrier plate and of a friction lining fastenedthereto. The brake pad is pressed against a brake disc during a brakingoperation. The two adjustment spindles are provided with an externalthread and are screwed in each case into a threaded bore of the bridge.

In the event of wear of the friction lining, a wear adjustment deviceassigned to one of the adjustment spindles serves, by rotating saidadjustment spindle, to advance the brake pad in the direction of thebrake disc such that an air gap between the brake pad and the brake discis always kept substantially constant.

For safety reasons, the friction lining should not fall below a minimumthickness, wherein a so-called wear sensor is embedded, in effect as analarm sensor, in the friction lining. A corresponding signal istriggered when the wear sensor comes into contact with the brake disc.Here, the wear sensor is positioned such that a minimum friction liningthickness remains.

In practice, however, problems often arise in that such signals aredisregarded and the vehicle continues to be used, such that the frictionlining becomes worn beyond the maximum admissible extent.

For design reasons, the adjustment spindles, which are guided in thebridge and which are axially adjustable relative thereto, are limited interms of their length, such that in the event of a further advancingmovement, the adjustment spindles are screwed out to such an extent asto become disconnected from the bridge. Thus, the adjustment spindlescan no longer perform the actual braking function, specifically thetransmission of the braking force to the brake pad, which ultimatelyleads to a total failure of the disc brake.

The stated problems arise not only in the event of alarm signals beingignored but also in the event of failure of the signal transducer, thatis to say of the stated wear sensor.

The invention is based on the object of further developing a disc brakeof the generic type such that the operational reliability thereof isimproved with little outlay in terms of design and manufacture.

This and other objects are achieved by providing a disc brake having abrake caliper which engages over a brake disc, a brake-applicationdevice which is arranged in the brake caliper and which serves forpressing brake pads against the brake disc, and at least one adjustmentspindle which is rotatably mounted, by way of a corresponding thread, ina bridge of the brake-application device. A wear adjustment device,which is positioned in the brake caliper, substantially compensates awear-induced change in an air gap between the brake pad and the brakedisc by way of an axial adjustment of the adjustment spindle. Theadjustment spindle has, on its outer side, at least one axial groove,which is limited in terms of its length in the direction of thebrake-application device and into which a stop, which is axially fixedwith respect to the bridge, engages in a relatively displaceable manner.

A disc brake designed within the scope of the invention offers assurancethat the adjustment spindle is not screwed out of the bridge for anyreason.

For this purpose, the axial groove, which is formed into the outer sideof the adjustment spindle and which is limited in terms of its length,forms a captive retention device in correspondence with a stop which isaxially fixed with respect to the bridge and which engages into saidaxial groove.

This stop, which is arranged on that side of the bridge which faces awayfrom the brake pad, may be formed by a positive-locking element, whichmay be provided in a variety of forms. Examples here are a fitted key ora ball, which is fixed to a suitable component of the wear adjustmentdevice.

The component is preferably formed of a drive wheel which is held in anaxially secured but rotatable manner on the brake caliper, specificallyon the side of the brake caliper which faces toward the brake pad.

Here, the drive wheel is preferably a constituent part of asynchronizing device, which is used when two adjustment spindles areprovided and arranged parallel to and spaced apart from one another, andwhich are to be adjusted uniformly, that is to say synchronously.

In this case, both adjustment spindles are equipped with in each caseone drive wheel and are connected to one another a power transmissionbelt, for example a linked chain or a toothed belt. The drive wheels arethen equipped with corresponding teeth.

Here, the stop which is in engagement with the axial groove performs notonly the stop function but also the function of a driver for torquetransmission, by which driver the force required for the wear adjustmentis transmitted from one adjustment spindle to the other.

According to a further concept of the invention, provision is made forthe length of the axial groove to be dimensioned such that theadjustment spindle can be screwed out only as far as a point at which apredefined minimum thickness of the friction lining, when the latterbears against the brake disc, is reached. Thus, in combination with awear sensor, redundancy is achieved which significantly improvesoperational reliability.

It is also notable that the invention can be realized with littleoutlay, basically even in a cost-neutral fashion, if the stop is anintegral constituent part of the synchronizing device.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of one ormore preferred embodiments when considered in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a part of a disc brake according to an embodiment of theinvention in an exploded illustration; and

FIG. 2 shows a section through the assembled part of the disc brakealong the line II-II in FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

The figures illustrate, as a part of a brake-application device of adisc brake for a commercial vehicle, a bridge 1 which can be positionedin a brake caliper of a disc brake and by means of which brake pads canbe pressed against a brake disc.

For this purpose, two adjustment spindles 3, which are arranged parallelto and spaced apart from one another, are held in the bridge 1, on oneend of which adjustment spindles there are mounted thrust pieces by wayof which the brake pads are pressed against the brake disc in the eventof a displacement of the brake-application device.

An axial adjustment of the adjustment spindles 3 for the compensation ofa wear-induced change of an air gap (clearance) between the brake padand brake disc is possible by means of a wear adjustment devicepositioned in the brake caliper.

For this purpose, the adjustment spindles 3 and the associated bores ofthe bridge 1 are provided with intermeshing threads 5 such that, in theevent of an actuation of the wear adjustment device, the adjustmentspindles 3 are moved axially in the direction of the brake pad by beingrotated.

To ensure a uniform adjustment of both adjustment spindles 3, asynchronizing device 2 is provided, the latter having a belt drivecomposed of two drive wheels 6 and a power transmission belt 7, whereina drive wheel 6 is held in a rotationally conjoint manner on eachadjustment spindle 6 and in an axially secured but rotatable manner on abearing point of the bridge 1.

The drive wheels 6 are arranged on the side of the bridge 1 facingtoward the brake pad, with a closure plate 4 which closes off theinterior of the brake caliper in the leadthrough region of theadjustment spindles 3. To seal off the leadthrough region, there isconnected to the closure plate 4 a bellows 19, which bears by way of asealing surface against the adjustment spindle 3 and which, opposite thedrive wheel 6, bears a seal 14 with integrally formed tongues 20.

According to the invention, each of the adjustment spindles 3 has, onits outer side, axial grooves 11, which are limited in terms of theirlength in the direction of the brake application device and into whichthere engages a stop 10 which is axially fixed with respect to thebridge.

In the example, the stop 10 is composed of a ball which is held in afreely rotatable manner in the drive wheel 6 and in the axial groove 11.In the design variant illustrated, three axial grooves 11 are providedin each adjustment spindle 3, said axial grooves being arranged offsetwith respect one another at an angle of 120°.

As can be very clearly seen in particular in FIG. 1, the drive wheel 6is of two-part form and is composed of an inner wheel 9, in which thestops 10 are held, and an outer wheel 8 into which the powertransmission belt 7 engages in a positively locking fashion.

The inner wheel 9 has axially projecting lugs 15 which are distributeduniformly about the circumference and which each have an externaltoothing 16 (FIG. 1) and which engage into an internal toothing 17 ofthe outer wheel 8, such that very precise setting of the adjustmentspindles 3 relative to one another is possible during pre-assembly ofthe synchronizing device 2.

For the securing of the drive wheel 6 against axial displacement, anabutting clamping ring 13 is provided on the face side facing away fromthe inner wheel 9, and a clip 12 is also provided opposite, said clipbeing held in positively locking fashion on the bridge 1 and engaging onthe drive wheel 6. The above-mentioned tongues 20 and the seal 14 restsealingly in, in each, case one axial groove 11. The power transmissionbelt 7 is kept under tension by way of a tensioner 18 that bears againstat least one strand of the power transmission belt.

LIST OF REFERENCE NUMERALS

1 Bridge

2 Synchronizing device

3 Adjustment spindle

4 Closure plate

5 Thread

6 Drive wheel

7 Power transmission belt

8 Outer wheel

9 Inner wheel

10 Stop

11 Axial groove

12 Clip

13 Clamping ring

14 Seal

15 Lug

16 External teeth

17 Internal teeth

18 Tensioners

19 Bellows

20 Tongue

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

What is claimed is:
 1. A disc brake for a commercial vehicle,comprising: a brake caliper engageable over a brake disc; a brakeapplication device arranged in the brake caliper for pressing brake padsagainst the brake disc, the brake application device including at leastone adjustment spindle rotatably mounted in a bridge via a threadedcoupling; a wear adjustment device positioned in the brake caliper forcompensating a wear-induced change in an air gap between the brake padand the brake disc via an axial adjustment of the at least oneadjustment spindle, wherein the adjustment spindle has, on an outerside, at least one axial groove, the axial groove being limited in itslength in a direction of the brake-application device, and a stopaxially fixed with respect to the bridge, the stop engaging into theaxial groove in a relatively displaceable manner.
 2. The disc brakeaccording to claim 1, wherein the adjustment spindle comprises multipleaxial grooves arranged parallel to and spaced apart from one another. 3.The disc brake according to claim 2, wherein the axial grooves arearranged at uniform angular intervals with respect to one another. 4.The disc brake according to claim 1, wherein the stop comprises a ballor a fitted key.
 5. The disc brake according to claim 4, wherein thestop is rotatable together with the adjustment spindle relative to thebridge.
 6. The disc brake according to claim 1, wherein the stop isarranged on a drive wheel of a synchronizing device by which twoadjustment spindles are synchronously adjustable.
 7. The disc brakeaccording to claim 1, wherein the stop is rotatable together with theadjustment spindle relative to the bridge.
 8. The disc brake accordingto claim 1, wherein the axial groove has a length limit such that theaxial groove is screwable out of the bridge only to a point at which thebrake pad, in a braking position, bears with a minimum thickness of afriction lining material of the brake pad against the brake disc.
 9. Thedisc brake according to claim 6, wherein the synchronizing device isarranged on a side of the bridge facing toward the brake disc.
 10. Thedisc brake according to claim 6, wherein the drive wheel is mounted in arotatable but axially secured manner on the bridge.